Color inkjet printers are already well known as typical liquid ejection apparatuses. Color inkjet printers are provided with a print head, which is an example of an inkjet-type ejection head, for ejecting ink, which is an example of a liquid, from nozzles, and are configured to record images and text, for example, by ejecting ink onto print paper, which is an example of a medium.
The print head is supported by a carriage such that the nozzle face in which the nozzles are formed is in opposition to the print paper, and moves (performs “main scan”) in the width direction of the print paper along a guide member, ejecting ink in synchronization with this main scan.
Moreover, color jet printers that allow so-called borderless printing, in which the entire surface of the print paper is printed on, have become popular in recent years because, among other things, they allow output results of images like photographs to be obtained. Borderless printing for example allows printing to be carried out by ejecting ink without leaving borders at the four edges of the print paper.
However, since printing is performed over the entire surface of the print paper with borderless printing, it is important to ensure that there are no margin portions at the edges of the printed print paper. In order to achieve this, it is effective to adopt an approach of: preparing print data that is slightly larger than the printing, or in other words, print data that is provided with a certain margin compared to the size of the print paper; and printing on the print paper according to this print data, in order to give due consideration to the possibility that the print paper may be fed at an angle (fed in a skewed state).
Further, in order to mitigate the problem brought about by the above-mentioned approach in that ink is wasted by printing in regions outside the print paper, an effective measure is to detect the position of an edge of the print paper using a sensor and vary a starting position and/or an ending position for ejecting ink according to the position of the detected edge.
However, while executing such a measure, it is possible that a situation may occur in which detection of the positions of the left and right edges becomes shifted due to a detection error of the sensor when the sensor is near the top and bottom edges of the print paper. This situation is described using FIG. 16 and FIG. 17. FIG. 16 is a schematic diagram showing the positional relationship between the print paper and the illumination spot of the left-and-right-edge detection sensor. FIG. 17 is an explanatory diagram illustrating the shift in the detected positions of the left and right edges depending on the position of the illumination spot of the left-and-right-edge detection sensor.
According to FIG. 16, the illumination spot of the edge detection sensor (here, for detection of the lateral edges) on a print paper P moves in a main scanning direction while causing changes in the amount of light received by being blocked by the edge of the print paper P, and thereby the edge is detected by referencing a set value (i.e., a threshold value).
However, as indicated by Spot Position 1 and Spot Position 2, a difference in the area on the print paper P, which blocks the spot, occurs even at similar positions at the left and right edges in the main scanning direction (in this example, the area of Spot Position 2 is half the area of Spot Position 1). In other words, when detecting the left and right edges at the top or bottom edge portions of the print paper as shown by Spot Position 2, it is necessary for the spot to move further in the main scanning direction (inward into the print paper) in order to attain a light-blocked area in the print paper, which is similar to that of Spot Position 1, and reach the threshold value. In this example, the spot diameter attains the same light-blocked area (i.e., threshold value) at the position (shown by the dotted circle) which is inward of the print paper P.
As shown in more detail in FIG. 17, at Spot Position 1, or in other words, at positions which do not include the top or bottom edges of the print paper P in the paper feed direction of the print paper P, the amount of light received by the edge detection sensor reaches the judgment threshold value when the illumination spot reaches edge position PE in the main scanning direction of the print paper P. However, at Spot Position 2, or in other words, at positions which include the top or bottom edges of the print paper P in the paper feed direction of the print paper P, the amount of light received by the edge detection sensor does not reach the judgment threshold value described above even when the illumination spot reaches the edge position PE in the main scanning direction of the print paper P, as described above. As the edge detection sensor moves further in the main scanning direction, or in other words, as the illumination spot moves further in the main scanning direction and the amount of light received by the edge detection sensor increases, the amount of light received by the edge detection sensor at a position C, which is much inward from the print paper edge PE, reaches the judgment threshold value, and this position is mistakenly identified as the edge position of the print paper P.
Due to this, the left and right edges are mistakenly detected further inward of the print paper P when the sensor is near the top or bottom edges of the print paper, and the starting position and ending position for ink to be ejected are determined based on these misdetected positions of the left and right edges; therefore, no ink is ejected in these portions, and margins are formed in these portions.
Situations may also arise in which the positions of the left and right edges of the print paper are not detected due to a detection error in the sensor due to the position of the print paper, or some other reason.
In such situations, there is the possibility that a margin might mistakenly be created in the print paper if the starting position and the ending position for ejecting ink in the next main scan are determined simply by using information about the positions of the left and right edges detected during the immediately preceding main scan, without changing the procedure for determining the starting position and the ending position. This problem is likely to occur especially in cases where the print paper is supplied at an angle (skewed).
The present invention was arrived at in light of the foregoing issues, and it is an object thereof to achieve a liquid ejection apparatus, a liquid ejection system, and a liquid ejection method that can appropriately set starting positions and ending positions for ejecting liquid.